This invention relates to a helical conical spring lock-washer, and more particularly to a helical conical spring lock-washer which is designed to further improve the effect obtainable by the "Conical Spring Washer" which is the subject of U.S. Pat. No. 4,103,725, and also to further reduce the production cost of such washer, as well as to a method of formation of such lockwasher.
Hithertofore, as spring lock-washers, spring washers of rectangular cross section, conical spring washers and internal or external toothed lock-washers have been known.
The spring washer is produced by winding a flat steel wire into a continuous spiral and cutting the spiral by each turn of the spiral. The spring washer is the least expensive, with respect to material cost and production cost, of known washers for the prevention of loosening. However, the non-loosening effect obtainable by this type of washer is quite doubtful and some automobile makers have completely abandoned the use of such washer. The reason for such abandonment of use is due to the facts that unstable induced axial forces are developed by the rotation of the washer together with a fastening device such as a bolt or nut during the tightening of the fastening device, and that insufficient spring effects remain after the tightening of the fastening device.
In addition to the spring washer, there are conical spring washers and internal or external toothed lock-washers which are produced from a steel sheet or steel strip. Although these washers exhibit stable induced axial forces and an excellent non-loosening effect over the spring washer, the yield rate of these washers is 40-50%, and these washers thus have the disadvantage of considerably high production costs due to required pressing operations.